Straits Substation
St. Ignace, MI

MJE provided labor, construction equipment, and materials to assist in the repair of self-contained fluid filled (SCFF) cables which join the upper and lower peninsula power grids under the Straits of Mackinac. This basic cable design was developed in the 1920’s and uses dielectric fluid under pressure to maintain insulation integrity. Four of the 138 kV cables were installed in the early 1970’s, and due to unsecured movement and contact with below grade rock formations at both ends of the cables, the cables experienced problems with fluid leaks near the cable pothead risers where the below grade system transitions to overhead transmission lines. The core of the Straits project involved excavating the ends of the cables along the shorelines, removing and replacing the leaking land section of the cables, and splicing the new cable end section along with a new termination structure on the end of the existing submarine cables. Existing data concerning cable anchor blocks was incomplete, so MJE did exploratory excavation. The circuits are critical to the Upper Peninsula’s grid so the timeframe for the repairs was compressed. The adjacent circuits shared the same existing deadend structure so maintaining one energized circuit while the other was being repaired was very challenging. MJE also worked around the presence of several endangered plant species and known contaminated soils at Point LeBarbe Station. MJE also hired dewatering and water treatment specialists to ensure that water present in the excavations was properly maintained, contained, treated, and disposed in a safe manner. The existing wood structures at both riser stations were deteriorating and ATC decided to replace these structures with new steel structures and added a new high security fence. MJE’s drilling, substation, and transmission crews all completed portions of the work.